The present invention refers to an improved hydraulic vehicle shock absorber intended to provide an optimum damping action only when there is a real need thereof and then to a well controlled level. In fact, a hydraulic vehicle shock absorber according to the invention comprises a cylindrical chamber which is closed at one end and in which is axially slidably guided a piston member supported by a piston rod and at its peripheral surface carrying a surrounding non-slotted elastic ring element, the peripheral piston member surface being conically converging in a directional wave from the closed chamber end and the inner surface of the ring element also conically converging in the same direction, the ring element furthermore being axially slidably mounted on the piston member between a first rigid abutment at the end of a said member closest to the closed end of the chamber and a second rigid abutment on the piston member at a spacing from the first abutment exceeding the axial length of the ring element.
Motion or shock absorber designs with co-operating conical surfaces are known in several connections. Thus DE 196 42 806 C1 shows such a design with a co-operating conical surfaces in connection with a pneumatic motion damper for e.g. a glove compartment lid. On a piston with conical outer surface slidably guided in a cylinder is carried a correspondingly conical sleeve like sealing being slightly axially movable on the piston and on its auto-surface having a sealing collar engaging the surrounding cylinder wall. The damping or absorbing fluid, in the present case air, therefore can not pass between the sealing sleeve and in the cylinder wall but only through a restricted channel in the conical surfaces when the same are engaging each other during the piston rod movement out of the cylinder. In the opposite motion direction of the piston the mutual engagement of the conical surfaces is stopped very rapidly due to the material stresses in the ring element and a greater cross sectional area is made free to the absorbing fluid. Mutually co-operating conical surface also may be used to provide in a cylindrical chamber a suitable bearing force against the cylinder wall and in this manner by friction to provide a damping action on a motion, such as described in FR A 1 077 611. U.S. Pat. No. 2,912,069 describes how an elastic insert body provided with a conical surface may serve as a valve member in a shock absorber structure in order to make the shock absorber more silent in operation. EP 0 198 A2 describes a piston- and ring-arrangement in a shock-absorber design in order to provide for as few parts as possible, namely two. Finally, FR A 2 493 443 shows mutually co-operating conical surfaces which provides for the expansion of a break means creating a friction force against a cylinder wall.
Most of the present vehicle shock absorber structures of hydraulical type usually comprise a piston member carried by a piston rod and provided with central penetrating bores or channels with a plurality of valve means and spring means. A drawback of such structures is that they necessarily show a non-unessential time lag in their operation as the same time as the fluid or oil passing through the piston becomes heavily agitated which leads to the formation of foam and generation of heat. Said generation of heat in its turn leads to changes of the viscosity of the absorbing fluid and therefore cooling measures often are required. In motorcycles and particularly in snow mobiles there occurs an inconvenient phenomenon in the form of so-called memory action of the shock absorbers. If for instance the front steering skis of the snow mobiles are mounted in spring struts provided with shock absorbers it is essential that the damping of the outward movement of the spring strut after a compression occurs distinctly but extremely fast since otherwise in a new closely following compression spring movement the shock absorber has not yet allowed the spring strut to extend completely. In a plurality of such compressions of the spring strut following closely after each other in a regularly uneven path or the like in various types of country driving, the spring strut finally may stop into a completely compressed position and thus act as being fully rigid. Since it is important that the spring absorbs most of the impact force against a obstacle, the shock absorbing or damping action usually is selected small at the compression movement, to a magnitude of about 10%, while a shock absorbing or damping action of about 90% is desired at the movement outwardly. The shock absorber according to the invention may also advantageously be used in most other vehicles than the above-stated.